Rockwell Automation 1772-L8_LW_LWP_LX_LXP,D17726.5.8 User Manual - Manual (Page 16)

Fundamentals of a
Programmable Controller
Chapter 2
2-2
Systems run by programmable controllers operate in much the same way.
Programmable controllers can perform many of the functions of traditional
controls. Input sensing devices report machine conditions; output devices
respond to commands.
Control Panel Programmable
Machine
Sensing
Devices
Output
Devices
11592
Conditons
Controller
Action
Command
Wiring between the machine and the controller provides electrical paths
from the sensing devices to the controller and from the controller to the
output devices.
However, instead of wiring relays together to produce a desired response,
you simply tell your programmable controller how you want it to respond.
A program tells your programmable controller what you want it to do. A
program is nothing more than a set of instructions you give the
programmable controller telling it how to react to certain conditions within
the machine.
A typical programmable controller system usually consists of four
major sections:
processor
input
modules
output modules
power supply
Programmable Systems
The Four Major Sections